Lost in the flood


This morning’s NASA Earth Observatory image of the day shows the impact of last week’s heavy rain in Christchurch and Banks Peninsula on the sea around. The light blue colours show sediment washed off the land. If you visit the EO page, they provide a helpful reference image: the region snapped from space in late February, when there’s no sign of any sediment at all.

The heavy rain brought flooding to many parts of Christchurch, as NASA notes:

Christchurch’s flood control infrastructure has been under increasing pressure in recent years because a series of earthquakes struck the area in 2010 and 2011. According to University of Canterbury researchers, the quakes caused land in some areas to drop, while narrowing and uplifting certain river channels. The result is an increased risk of flooding.

This rainfall map from NIWA shows rainfall over the last 15 days (right) compared with the average for the same period (left) and the anomaly (centre). The rain event is immediately obvious as the blue thumb sticking out of the South Island east coast:


The Weather Underground’s Christopher Burt provides numbers for the storm:

The powerful storm pounded the Christchurch area between March 3-5 with wind gusts up to 119 km/h (74 mph) and rainfall of 151.6 mm (5.97”) as officially measured at Christchurch’s weather station. Of this amount 100 mm (3.94”) fell in just a single 24-hour period on March 4-5. The suburb of Lyttelton received 160 mm (6.30”) in 24 hours and other suburbs reported storm totals of 170 mm (6.70”). The normal monthly rainfall for Christchurch in March is just 45 mm (1.77”).

For a selection of pictures, see these galleries at Stuff.co.nz: Christchurch, Lyttleton and Banks Peninsula.

The severe flooding in parts of Christchurch – notably the “Flockton Basin” – was caused or made worse by a number of factors. The earthquake sequence caused ground levels to fall by up to half a metre in parts of the eastern suburbs and along the Avon River (see map here), raised and narrowed river and stream beds and damaged or destroyed storm water infrastructure. Add to that a heavy rainfall event that would have taxed the drainage system in pre-quake times, not to mention the tail end of a sequence of high spring tides causing water to back up in the estuary, and you have all the makings of a historic flood event.

Local and national politicians have rushed to promise action to address the flooding, but Christchurch’s problems will not be solved by a crash programme to defend homes that now flood every time there’s a rainstorm. Continuing sea level rise and increasing rainfall intensities — both already observed and projected to get much worse — suggest that serious consideration should be given to managed retreat in some areas, rather than rebuild and defend. How high should you make a stop bank when you expect sea level in a hundred years time to be a metre higher than now?

Christchurch is facing the sort of problems that all coastal cities are going to have to confront over coming decades, brought forward by the earthquake sequence that caused so much death and destruction. Unfortunately for the citizens of the city, the earthquake recovery programme is being overseen by Gerry Brownlee, a cabinet minister who is on the record as a climate sceptic. If he fails to consider the big picture, and neglects to plan for a future when the waters have risen far above today’s levels, then Christchurch will be even deeper trouble every time it rains old women and sticks1.

[Brooce, at his best.]

  1. Mae hi’n bwrw hen wragedd a ffyn – It’s raining old ladies and sticks: Welsh idiom. []

34 thoughts on “Lost in the flood”

  1. Leanne Dalziell was very good on this on Nine to Noon on Friday. She said the council started working on a new district plan straight after the quake. But the national standard is for a 50cm sea level rise, and the Chch City Council’s had advice to prepare for a 1m sea level rise.

    She noted that there should be a National Policy Statement from central govt on this… that the CCC shouldn’t have to “go it alone” and that with climate change the whole country should be getting much better prepared.

    here’s the link to her interview. http://www.radionz.co.nz/audio/player/2588155

    1. Lianne Dalziel has some rather more urgent matters to consider with the Flockton basin area. We are not talking 100 year floods here, we are talking about several floods since the earthquakes that have required people to make up to three separate claims for full carpet replacement. Most insurers have had enough and are refusing to re-insure these properties.

      Unfortunatley, unless your house is on piles, just lifting it is not an option.

      John Key intimated recently that Red Zoning the area may be on the cards.

      1. “Red zoning” = managed retreat. At least the earthquake recovery has given Christchurch one tool that might deal with the worst of the problem. However, easing the plight of residents in the Flockton basin – which is well worth doing, and quickly – will not solve the longer term problem. Rebuilding a city on an estuary and swamp when multi-metre sea level rise is expected is not smart.

  2. The floods in Christchurch is a prime example of what happens when politicians do not take advice from experts in the field. New Zealand has some of the finest climate scientists in the World and many of them use Christchurch to go to Antarctica. The knowledge that sea levels are likely to be much worse than the IPCC predictions is not new but as they say ‘There are none so deaf as those that won’t listen’ Gerry Brownlee is a denier and was unlikely to make decisions that got in the way of making money.

    1. How are the floods in Christchurch anything to do with not heeding advice of experts?

      The Flockton Basin area floods every time it rains. It is due to the lowering of the land level and the damage to the rivers that allow the water to drain away

      1. If there had been a proper assessment of the situation after the earthquake the longer term dangers of sea level rise would have been made. This would have meant a larger red zone and the people would have been moved. Avoiding the situation only drags out the problem longer and the people will have to move anyway. You know Christchurch put the gauge on one meter and look at the city. http://flood.firetree.net/

  3. Back in 2008, I attended 1-day symposium for local town planners and related folks “Preparing for Sea Level Rise in the Bay Area – A Local Government Forum”. It started with (serious) scientists from Scripps and USGS explaining what was known, what wasn’t, and the best estimates of SLR over next 100 years. Then there were talks by towns, taking about both mitigation and adaptation, talks by experts in building dikes, sewage systems ,etc. (Sewage systems are very tricky, since they want to be downhill from those served, and preferably not below sea level).

    We split into teams, and got descriptions of imaginary towns, and spent and hour or two laying out 50-year+ plans. Even with that, one could see ugly, ugly politics and the difficulties of planning under such uncertainty. For example, if you think some infrastructure’s life is X years, you would naturally want to leave it there for X years, and plan for its replacement (life =- Y), likely uphill/further inland,for it to survive for Y years more … and the more uncertainty there is in SLR, the harder this gets. Likewise, people’s homes in awkward places.

    Opinion: it is almost criminal for a government to tell its constituent localities anything but the best scientific estimates available, as this problem is hard enough even with them. But with fantasies, it is close to impossible to do a good job.

  4. I seem to recall the land has subsided about 60mm. Given houses are at least 150mm above finished ground level, this would only account for a small part of the flooding. The main cause must be broken drains, altered river flow and extreme weather. Rising sea levels will be a future factor.

  5. As best as I can tell, SLR planning (combined with subsidence) is more challenging than that for dealing with floods and storms, in the following sense;

    1) In planning for floods/storms (tornadoes/earthquakes) one is trying to engineer local infrastructure to survive rare events with some expected occurrence rate … and be willing to take damage for rarer worse events.

    2) So, if one puts up sea walls against storm surge, and they get overtopped by a really rare event (like Hurricane Sandy), it’s a mess, but then at least the water eventually flows downhill back to the ocean.

    3) The SLR doesn’t go away, and people can certainly live below sea level, but if one looks carefully at the population maps of the Netherlands, most of the development is inland, not right at the shore, and when they built the ZuiderZee works, it actually shortened the length of defenses.

    4) Although I’ve visited Christchurch and enjoyed it, I don’t know about the local geology, except that it gets earthquakes, bad enough.

    Miami doesn’t have earthquakes, but certainly sees hurricanes, and if you want to see trouble, try this. Among other things, saltwater incursion is a real problem, and sea walls don’t help much, because S. Florida is porous limestone like swiss cheese, so the water comes in underneath. Unlike Christchurch, there is not much “uphill” anywhere nearby.

  6. The point that I was trying to make is that the rebuild is a multi billion affair and the city CBD has probably fifty years of life.Would it have been wiser to move it to higher ground to give it a longer life? They could have had a bigger red zone and moved a lot of the lowest lying residents to higher ground.

    1. The red zone process comes at a cost, namely the financial cost of the government/taxpayer financing the compulsory acquisition of land and the subsequent social unrest in rehoming these people.

      These costs are already in the billions. I suspect there was a deal with the insurance companies in exchange for a guarantee of future insurance of the country

      The red zone process was that deal with insurance. The government are probably reluctant to engage in further compensation.

    2. Yes, that is the right point. The real issue is:
      a) Such issues always have to get handled by local planners, with complex politics, and as noted, insurance companies have opinions, and given that they are actually paid to price risk, folks like Munich Re and Swiss Re are among the most realistic of the big companies on impacts of climate change,

      b) But larger governments owe localities the best science advice they can get. it is hard enough, and all too easy for elected politicians to take short-term positions and transfer costs to the future.

  7. I guess for the decision makers of the last years in ChCh factoring the big picture of SLR and AGW into the frame was just too much. What they felt they were charged with is to come up with a plan to repair as much as possible what the earthquakes damaged. But of cause in a way the earthquakes would have been the ideal reason to actually factor the big picture in, and make solid plans for a long term future. When else do you get to re-plan an entire CBD and in a away a city.
    But perhaps it is also tied into insurance shortsightedness whereby payouts for repairs in situ are possible but relocation not? What would the insurance say if the government decided that relocation was inevitable anyway and the EQ demolition a way to get it paid for as part of an insured “incident”?? Very complex indeed! And very much time for the nation to work all this out.
    What will be the stance of the insurance industry towards SLR?? Will they simply refuse to renew insurance once an area become threatened by inundation in the short term future?

    Low lying areas of the North Island might get a taste of it all on the weekend to come:

    1. ew! That looks nasty! “batten down the hatches” we have been wanting some rain – but not quite like that!
      Just in time for the submissions to be in for SLR! 🙂 Should help to reinforce a point – storm surges etc. There has been a bit of work going on around town here completing stop banks etc around the river. Probably just in time I would say. Fortunately we are above it all. But then being on top of the Thames fault line…….. lol guess you can’t avoid some form of Natural hazard in the “shaky Isles”

      1. Yes, I have a student in Whiti who wants to document the potential issues for future SLR here as a paper. I think she might get some before/after footage of the weekends proceedings to help her make the point!
        Certainly keep and eye on the forecasts. It seems to be pretty much a direct hit for us here at the current forecast images.

    2. Insurance companies won’t pay more than they need to. They are, after all, commercial enterprises.

      The insurance companies will pay out for repairs only, even if the land is damaged beyond repair. This is because the land is not part of the insurance package. Land is dealt with by EQC.

      EQC are not paying out on land that has sunk by up to 50cm, even though it floods every time it rains.

      So you can’t really blame insurance companies for this.

      1. I should add that “repairs only” applies to property where it is more economic to repair than rebuild.

        The economics are costed only on getting the physical property back to its state before the event (e.g earthquake)

        No account is taken of the land, or any future environmental impacts such as SLR, future earthquake risk, or flooding. These issues may, however, impact on the future insurability of the house or the premiums charged.

        1. yes precisely and that is part of the problem obviously.
          The deal should perhaps be that the insurance companies pay what they are obliged to do, but the money is not wasted on repairing an untenable (beyond short term perhaps) situation. Instead the money is spend on relocation and re-building there. The land owner has the benefit of getting the relocation at least part-paid – thanks to the Earthquake. Without the Earthquake relocation is on the cards sooner or later anyway, sooner for the lowest lying suburbs, and then the cost would entirely fall onto land owners one must assume.
          So the earthquake was really a golden opportunity to turn a momentary calamity into a building block for future proofing a town through re-location. In then end, long term, that is all that can be done anyway. Sadly, unless our leaders make it happen, this opportunity will be lost as more valuable resources are squandered on sinking lands.

  8. I will be moving the boat out of the river tomorrow just in case its a big one. I posted a few days ago that 200 mm is OK but 350 mm washed all the boats away. The problem is that by the time you realise how much is falling its too late to go on the river..

    1. Which river? Of the northern rivers I know only the tidal reaches are navigable, but tidal reaches are not necessarily wide and take all the flood waters.

    1. February 2004 – the big rain. Yes I learned my boating first on that river and perhaps you know that on its southern bank is Fullers Rd though that road is vey recent. On the river there my grandfather had a two slip boat shed. I wonder occasionally if any boats he built are still in service. He was foolish enough, however, to believe that there was more money in farming than in the boating business his brothers carried on to do so well out of. The farm was covered in Kikuyu but to me it, or rather the river, was a place of magic.

    1. There is one solution that allows construction at beach sub-division – transportable homes. The local Hauraki District council has this provision in its current plan – allowing only homes that are transportable to be sited at beach front sections. There are some very liveable ones being made now. I have one on a beach property so am unfazed by SLR.
      They only take a day to move on or off a site.
      I’m surprised that the govt has not used them as a partial solution to housing the people displaced in ChCh. They take about 6 weeks to make off site. Transport them to where-ever. Connect up to water (a hose from a tap suffices – or rainwater tank supply far more self sufficient) and power from builders pole – or better still pv array they have very little electrical demand). Biggest problem is sewage- temporary tankage -separating grey water. But composting worm disposal and other septic solutions are also available.

  9. It looks like an obvious solution to future sea level rise and eroding shorelines but I suspect the modest dimensions will not suit those whose idea of a ‘bach’ by the sea is a grandiose two storey mansion-lite.

    I’m looking at you, Omaha…

    1. 🙂 yes I know what you mean – however I am reliably informed that a very “wealthy” individual who wouldn’t dream of rubbing shoulders with the hoi polloi at Omaha has a go-home on his large property north of Helensville. 😉

Leave a Reply